Steering valve/system operation—five-port valve – John Deere 318 User Manual

Page 386

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STEERING VALVE/SYSTEM OPERATION—FIVE-PORT VALVE

Function:
Supply pressurized oil to the proper side of the
steering cylinder to turn the wheels, when the engine
is running.

Theory of Operation:

NOTE: Right-hand turn shown.

All external oil flow from the transmission is routed
through the steering valve. The steering valve is an
open center type valve. The “five-port” design
provides “power beyond” to the auxiliary hydraulic
systems only after satisfying steering valve needs.

The steering valve consists of a self-centering fluid
control valve section (E) and a fluid metering section
(H). These are hydraulically and mechanically
interconnected inside the valve (C).

NEUTRAL:
Whenever the steering wheel (G) is released, the
centering springs (D) return the control valve section
to the center (neutral) position. In this position,
charge pressure oil entering the steering valve
through port “IN” is allowed to flow through the
control valve section and out through port “AUX”.
When in neutral position, the control valve prevents
charge pressure oil from entering the fluid metering
section.

POWER TURN:
As the steering wheel is turned to the right, the
control valve section is shifted by the drive link
assembly (B). This shifting opens the steering cylinder
ports “RT” and “LT”. Oil flow to auxiliary hydraulic
systems through port “AUX” is reduced giving the
steering valve priority over the auxiliary system
components.

Oil flows from port “IN” directly to the inlet of the
control valve section. As the steering wheel is turned,

charge pressure oil is routed through the control
valve section to the fluid metering section. Metered oil
is routed to port “RT” on the steering cylinder. Return
oil from the other end of the steering cylinder is
routed back to port “LT”, through the control valve
and “OUT” port, returning to the transmission.

When the rotation of the steering wheel stops, the
centering springs (D) move the control valve section
back to the center (neutral) position, and will remain
there until the steering wheel is moved again.

MANUAL TURN:
If hydraulic pressure is lost, the machine can still be
steered without hydraulic assistance. All components
still function the same with the exception of the fluid
metering section (H). The fluid metering section now
acts as a pump, moving oil from one side of the
metering section to the other as the steering wheel is
turned.

When the rotation of the steering wheel stops, the
centering springs move the valve back to the center
(neutral) position, and will remain there until the
steering wheel is moved again.

STEERING CYLINDER OPERATION:
The steering cylinder is a double-acting design.

One end of the cylinder is attached to the frame
which prevents the cylinder from moving. The rod end
is attached to the steering arm/spindle.

As pressurized oil enters the cylinder, the piston and
rod move, moving the steering arm, causing the
machine to turn.

To turn in the other direction, pressurized oil is
applied to the other port, moving the cylinder in the
opposite direction.

MX,159026010,2 -19-24APR95

Theory of Operation/Steering Valve/System Operation

TM1590 (17MAY95)

260-10-2

316, 318 & 420 Lawn and Garden Tractors

020895

260

10

2

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This manual is related to the following products:

316, 420